Herror ::detect_edge_segments (
    Hobject Image,
    const HTuple &SobelSize,
    const HTuple &MinAmplitude,
    const HTuple &MaxDistance,
    const HTuple &MinLength,
    HTuple *BeginRow,
    HTuple *BeginCol,
    HTuple *EndRow,
    HTuple *EndCol
)
HTuple HImage::DetectEdgeSegments (
    const HTuple &SobelSize,
    const HTuple &MinAmplitude,
    const HTuple &MaxDistance,
    const HTuple &MinLength,
    HTuple *BeginCol,
    HTuple *EndRow,
    HTuple *EndCol
) const
HTuple HImageArray::DetectEdgeSegments (
    const HTuple &SobelSize,
    const HTuple &MinAmplitude,
    const HTuple &MaxDistance,
    const HTuple &MinLength,
    HTuple *BeginCol,
    HTuple *EndRow,
    HTuple *EndCol
) const

Detect straight edge segments.

::detect_edge_segments detects straight edge segments in the gray image Image. The extracted edge segments are returned as line segments with start point (BeginRow,BeginCol) and end point (EndRow,EndCol). Edge detection is based on the Sobel filter, using 'sum_abs' as parameter and SobelSize as the filter mask size (see ::sobel_amp). Only pixels with a filter response larger than MinAmplitude are used as candidates for edge points. These thresholded edge points are thinned and split into straight segments. Due to technical reasons, edge points in which several edges meet are lost. Therefore, ::detect_edge_segments usually does not return closed object contours. The parameter MaxDistance controls the maximum allowed distance of an edge point to its approximating line. For efficiency reasons, the sum of the absolute values of the coordinate differences is used instead of the Euclidean distance. MinLength controls the minimum length of the line segments. Lines shorter than MinLength are not returned.

Parameters

Image (input_object)
 (multichannel-)image(-array) -> Hobject: HImage(Array) ( byte )
Input image.

SobelSize (input_control)
 integer -> HTuple.long
Mask size of the Sobel operator.
Default value: 5
List of values: 3, 5, 7, 9, 11, 13

MinAmplitude (input_control)
 integer -> HTuple.long
Minimum edge strength.
Default value: 32
Suggested values: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, 100, 110
Typical range of values: 1 <= MinAmplitude <= 255
Minimum increment: 1
Recommended increment: 1
Restriction: MinAmplitude >= 0

MaxDistance (input_control)
 integer -> HTuple.long
Maximum distance of the approximating line to its original edge.
Default value: 3
Suggested values: 2, 3, 4, 5, 6, 7, 8
Typical range of values: 1 <= MaxDistance <= 30
Minimum increment: 1
Recommended increment: 1
Restriction: MaxDistance >= 0

MinLength (input_control)
 integer -> HTuple.long
Minimum lenght of to resulting line segments.
Default value: 10
Suggested values: 3, 5, 7, 9, 11, 13, 16, 20
Typical range of values: 1 <= MinLength <= 500
Minimum increment: 1
Recommended increment: 1
Restriction: MinLength >= 0

BeginRow (output_control)
 line.begin.y-array -> HTuple.long *
Row coordinate of the line segments' start points.

BeginCol (output_control)
 line.begin.x-array -> HTuple.long *
Column coordinate of the line segments' start points.

EndRow (output_control)
 line.end.y-array -> HTuple.long *
Row coordinate of the line segments' end points.

EndCol (output_control)
 line.end.x-array -> HTuple.long *
Column coordinate of the line segments' end points.

Example
Htuple  SobelSize,MinAmplitude,MaxDistance,MinLength;
Htuple  RowBegin,ColBegin,RowEnd,ColEnd;

create_tuple(&SobelSize,1);
set_i(SobelSize,5,0);
create_tuple(&MinAmplitude,1);
set_i(MinAmplitude,32,0);
create_tuple(&MaxDistance,1);
set_i(MaxDistance,3,0);
create_tuple(&MinLength,1);
set_i(MinLength,10,0);
T_detect_edge_segments(Image,SobelSize,MinAmplitude,MaxDistance,MinLength,
                &RowBegin,&ColBegin,&RowEnd,&ColEnd);
Result

::detect_edge_segments returns H_MSG_TRUE if all parameters are correct. If the input is empty the behaviour can be set via ::set_system('no_object_result',<Result>). If necessary, an exception handling is raised.

Possible Predecessors

::sigma_image, ::median_image

Possible Successors

::select_lines, ::partition_lines, ::select_lines_longest, ::line_position, ::line_orientation

Alternatives

::sobel_amp, ::threshold, ::skeleton

Module

Image filters

Copyright © 1996-2002 MVTec Software GmbH